usb: cdnsp: Fix incorrect supported maximum speed

Driver had hardcoded in initialization maximum supported speed
to USB_SPEED_SUPER_PLUS but it should consider the speed
returned from usb_get_maximum_speed function.

Fixes: 3d829045

 ("usb: cdnsp: cdns3 Add main part of Cadence USBSSP DRD Driver")
Signed-off-by: Pawel Laszczak <pawell@cadence.com>
Link: https://lore.kernel.org/r/20210625102502.26336-1-pawell@gli-login.cadence.com
Signed-off-by: Peter Chen <peter.chen@kernel.org>